The 160m long Herrenknecht tunnel boring machine (TBM), named Mary after Mary Fergusson who the first female fellow of the Institution of Civil Engineers and grew up close to the site, was launched in April last year.

The new gas pipeline will be floated through the tunnel and replace an existing riverbed level pipeline.

National Grid project manager Steve Ellison said: Mary has done a brilliant job to date and we and our contractors are delighted to have reached the halfway point on the tunnel. There is still a lot more work to, do but I would like to say a big thank-you to the 40-strong team of engineers who have worked around the clock in very challenging conditions to get us to this important milestone.

“The machine has pretty much been operating 24 hours a day with the odd shut-down for repair or maintenance since the tunnelling work started on 6 April 2018. There are 20 engineers manning her on every shift and they work in very cramped and warm conditions, far below the river bed.”

Once the tunnel bore is completed it will be flooded to allow the new 1,050mm diameter pipeline to be floated through the tunnel and the water will remain in situ throughout the lifetime of the pipe.

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